1. Field of the Invention
The present invention relates to an apparatus for degasification of elastomeric material and the like in an extruder, particularly in an extruder utilizing a screw or worm.
2. Description of the Prior Art
When elastomeric material, such as a rubber compound, is fed into a hopper for a screw extruder, the material entrains and entraps air in the mixture. It is desirable to remove the air from the extrusion mass in order to avoid porosity in the rubber compound, especially if it is used for tire making. A typical extruder may also be provided with pins that project radially inwardly of the extrusion chamber for the purpose of kneading and mixing the material as it advances in the extruder chamber.
There have been several developments to date in an attempt to degasify elastomeric material. U.S. Pat. No. 4,538,917, issued Sep. 3, 1985 to Engelbert G. Harms, describes a screw extruder for elastomeric material having a degasification zone in which mixing pins are provided which have openings in the peripheral walls of the pins communicating with passages to vent the gases from the extrusion chamber.
U.S. Pat. No. 4,776,784, issued Oct. 11, 1988 to Martin Batiuk, describes an extruder for thermoplastic material in which a gas venting bore is arranged at an obtuse angle to the direction of flow and a screw is provided in the bore to be driven so as to continuously force the material back into the extrusion tube while allowing gas to escape.
Such prior art devices have disadvantages. For instance, the vented pins of Harms tend to clog up with rubber, preventing the air from exhausting. The Batiuk patent requires an expensive device with motors to drive each screw. Furthermore, the number of vents would be limited in view of the space requirement for each device. The vent device of Batiuk cannot serve the dual purpose of mixing.